This application claims the priority of PCT International Application No. PCT/EP99/03493, filed May 21, 1999 and German patent document 198 27 045.3, filed Jun. 18, 1998.
The invention relates to an apparatus for voltage measurement on a plurality of identical voltage sources.
A voltage source of this generic type is formed, for example, from one or more elementary battery cells, or from one or more elementary fuel cells.
One preferred field of application for such a voltage measurement arrangement is fuel cell systems, particularly H2/O2 fuel cells, which normally supply a cell voltage of approximately 0.5 V to 1.0 V. In order to achieve higher voltages, and thus higher power levels, individual fuel cells are connected in series to form a stack. When the fuel cells are being operated, it is necessary to ensure that they operate effectively and that the power supplied from the fuel cell stack does not force individual fuel cells to assume impermissible or dangerous operating states with a negative cell voltage, but that the cell voltages are maintained within a certain bandwidth, depending on the load state. Furthermore, it is desirable to be able to detect defects, which can lead to failure of a fuel cell, at the H2/O2 separation unit.
German patent document DE-Al 43 38 178 discloses an arrangement in which fuel cell stacks are connected in series in at least two parallel connected rows each having the same number of stacks, and in which the rows are split into arms of a bridge circuit and are connected to at least one evaluation arrangement which evaluates the voltage or current tapped off between the arms.
German patent document DE-C2 195 23 260 discloses a method for monitoring more than two identical voltage source units, in which contact tips are pressed against carbon contacts of fuel cell stacks which are combined to form blocks. However, the contact with the stacks is susceptible to vibration and, in particular is not suitable for use in a motor vehicle since, essentially only a stationary measurement is possible, and not continuous measurement in operational conditions.
One object of the present invention is to provide an arrangement for voltage measurement on a plurality of identical voltage source units, which is simple to fit, allows permanent voltage monitoring and flexible handling as well as simple and cost-effective matching to fuel cell stacks of different size.
Another object of the invention is to provide such a voltage measurement arrangement which is suitable in particular for use in mobile systems such as motor vehicles, as well as in stationary systems.
These and other objects and advantages are achieved by the voltage measurement arrangement according to the invention which includes contact-making means (xe2x80x9ccontactsxe2x80x9d) for voltage tapping, as well as an evaluation unit which is connected to the contacts. At least a number of contacts are physically combined in a contact unit. The contact unit preferably has a holder, electrically conductive contacts and electrical connectors, in particular pin-type plug connectors, for an evaluation unit or for an intermediate unit which is connected between the evaluation unit and the contact unit. It is particularly preferable for the contacts of the contact unit to have electrical spring contacts which can be detached from voltage source units with which contact is to be made.
In one advantageous arrangement the contact unit is in the form of a flat plate on which spring contacts are arranged approximately parallel to one another and projecting essentially at right angles from the longitudinal axis of the plate. The spring contacts are each firmly electrically conductively connected at one end to the respective associated electrical contact surface, and their free end can move at least in the direction of the longitudinal axis. In this case, it is particularly expedient for the contacts to have a corrosion-resistant metallic surface, at least in some places. It is advantageous for retaining surfaces for contacts to be provided for voltage tapping on the surface of the voltage source units.
In one preferred arrangement, the contact unit is arranged in a holder module such that it can be moved in the direction of its longitudinal axis. It is advantageous to arrange a number of contact units side by side in the direction of their longitudinal axis in a holder module, so that the contacts point outwards like a comb.
The contact unit expediently projects at right angles into a guide rail of a holder module in such a way that the contact unit can be moved along the guide rail parallel to the longitudinal extent of a housing, or parallel to a stacking direction of the voltage source units.
The evaluation unit is advantageously arranged in a housing. It is advantageous for the evaluation unit to be a central controller. In further advantageous refinement the evaluation unit has a unit for addressing and/or pre-processing of measurement data. It is particularly advantageous for an intermediate unit for addressing and/or pre-processing of measurement data to be connected between the contact unit and the evaluation unit.
In one particularly expedient refinement the contact unit is, in each case, at least indirectly electrically connected by means of a ribbon cable to the evaluation unit or to an intermediate unit which is connected between the contact unit and the evaluation unit.
In one particularly preferred refinement, each contact unit is allocated a segment of an intermediate unit. It is advantageous if, in addition to segments, the intermediate unit has a base unit which has at least one data bus interface and/or a microcontroller card. It is advantageous for the intermediate unit to have at least connecting means for a CAN bus.
The segment preferably has multiplexer units and electrical connection means allocated to the segment, to which connection means one or more contact units can be connected.
In one particularly preferred development, contact units are arranged at equal intervals along the longitudinal axis of the intermediate unit. Electrical connection means are preferably arranged at equal intervals along the longitudinal axis of the intermediate unit. Furthermore, regions of multiplexer units are preferably arranged at equal intervals along the longitudinal axis of the intermediate unit, and segments with multiplexer units and connectors are preferably arranged at equal intervals along the longitudinal axis of the intermediate unit.
It is particularly preferable for the longitudinal extent at least of segments, connectors and contact units to be staggered along the longitudinal axis of the intermediate unit. In this case the longitudinal extent of the contact units is a first length L1, the longitudinal extent of the regions of multiplexer units M is a second length LM, the longitudinal extent of the connection means is a third length L4, and the longitudinal extent of the segments is a fourth length L12, where L1 greater than L12 greater than L4 greater than LM.
Advantageously, the longitudinal extent at least of segments, connectors and contact units is staggered along the longitudinal axis of the intermediate unit and is arranged offset with respect to the stacking direction of the voltage source units so that the function of segments, connectors and contact units is maintained when shortened to a present stack length of the voltage source units.
In one advantageous embodiment, the holder module can be attached to the housing. In a further advantageous embodiment, the holder module can be attached to voltage source units.
It is expedient to provide attachment means of the intermediate unit in the housing with means to compensate for changes in the length of the intermediate unit and/or of the housing.
In one particularly advantageous refinement of the invention, the contact unit is connected to a discharge module, which forms a low impedance bridge for at least one voltage source unit. It is thus possible to deliberately discharge units in the voltage source units individually, or to discharge a number of such units in a stack, and to remove them safely, for example for maintenance purposes. It is particularly advantageous for the discharge module to be provided with means for connection of an electronic data processing device and, in particular, to be controllable by software.
The voltage source unit is preferably a fuel cell.
It is particularly preferable for retaining surfaces for the contacts to be provided for voltage tapping on the surface of the fuel cell. This makes contact with spring contacts particularly robust and reliable, in particular with respect to shock and/or vibration.
The modular construction of the apparatus according to the invention allows the apparatus to be used highly flexibly and cost-effectively.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.